1. Field of the Invention
The present invention relates to an helical antenna, and more particularly to a helical antenna having an antenna section configured by providing insulator bodies with helical conductors.
2. Description of the Related Art
FIG. 6 illustrates a conventional helical antenna. The helical antenna is configured by providing a strip or strips of helical conductor 12 around the circumference of a cylindrical molded body 11 of an insulating material (e.g. resin) having a hollow 11a in the center. The helical conductor 12 can be formed by winding a wire of copper or some other material helically or by printed wiring. In providing the helical conductor 12, a helical groove may be formed around the circumference of the cylindrical molded body 11 to prevent the conductor from slipping out of place. Such a helical antenna has an advantage of reduced overall length over a vertical antenna of a 1/4 wavelength or the like, consisting of a single conductor standing vertically. The presence of the hollow 11a in the center of the molded body 11 provides an additional advantage of reduced dielectric loss.
However, the conventional helical antenna, while its dielectric loss is reduced by providing the hollow 11a, involves the problem that thinning the thickness of the molded body 11 to further reduce its dielectric loss and its weight at the same time would weaken the strength or the molded body 11 and make it more difficult for the molded body to be drawn out of the mold.